The present invention relates to a slide swing bearing for bridges or similar structures and in particular to the form and arrangement of the slide member therefor.
Slide swing bearings to which the present invention is directed, generally comprise an upper and lower support member, one of which is movable, i.e., slideable with respect to the other. Interposed between these two support members is a slide element generally formed of polytetrafluoroethylene (PTFE) or similar plastic material is employed. In German Pat. No. 1,230,826, a large area PTFE plate or plates, are employed as the slide members. Such arrangement is disadvantageous in several respects. The slide members must be carefully encased and mounted to insure that the PTFE, which is known to be a flowable material, will withstand the support pressure. Such mounts are usually made of steel, however, the adaption of a steel to the exact diameter of PTFE plate proves to be very difficult because of the approximately ten fold difference in coefficient expansion of PTFE relative to steel. When the PTFE plates are very large it is practically impossible to carry such adaption out. In addition, there does not exist at this moment, particularly for the production of large PTFE plates, a production method which insures that the quality of the plate material remains constant over the entire surface of the plate. Still further, in order to provide for permanent lubrication, lubricating pockets are provided in the PTFE plates. Since such pockets are eroded and leveled due to the creep of the PTFE plate, the lubricant supply is used up or dissipated after a relatively short period of time.
In order to improve the permanent lubricating effect in the known PTFE plates, it is proposed from German Pat. No. 2,244,202, and German Offenlegungsschrift No. 2,252,289, to replace the lubricating pockets with lubricating channels which are open toward the sliding plane and allow post lubrication of the plates from the exterior necessitating an expensive treatment of the PTFE plate itself.
Other known proposals, in particular, the General Road Construction Circular 10/1965, Subject 5, Bridge Construction, published VkBl official part, Issue 5-66, page 130; Uetz, Hakenjos, Breckel, "Fundamental Relative to the Development and Testing of Bridge Supports Made of polytetrafluoroethylene", material test 10/1968, 1, pages 23, 24, disclose an increase in the lubricant supply by forming the sliding member of a single ring or several concentric rings whose interior is filled with lubricant. These rings act as radial seals for the lubricant, however, their production and the arrangement of such rings in the bearing are very expensive. It is to be noted that such bearings employing ring type slide members have, so far, not materialized in practice.
Finally, it is known from German Auslegeschrift No. 1,263805 and German GNS 7,2740,733, to divide a PTFE slide plate into single slide elements which are distributed over the contact surface with the supporting member and are secured in the base plate of the supporting member spaced from one another. The fastening of such slide elements, which take the form of circular discs is effected by mounting the same in appropriately shaped support plates, or by casting the slide elements into a plastic material which is adhered to the supporting member. The use of such slide elements requires an expensive and individualized treatment of the supporting member, and in addition, makes the permanent lubrication of the slide elements practically impossible, since the lubricant can escape from the spaces formed between the slide elements.
It is the object of the present invention to provide a sliding swing bearing having PTFE slide surface members which do not present the production application difficulties arising from the use of large area plates or rings made of PTFE and which is functionally equal to the known PTFE ring supports with respect to its permanent lubrication effect.